Why does anti-static masterbatch weaken? What should I pay attention to using anti-static masterbatch? When external or internal anti-static masterbatch is used for the antistatic treatment of materials, relative humidity, temperature, and surface concentration have certain effects on antistatic properties. This paper will analyze the influencing factors and treatment methods of anti-static masterbatch performance from the above aspects.
1. Influence of humidity and temperature
The antistatic effect of plastics treated with an anti-static masterbatch is related to the ambient temperature and humidity. The higher the humidity and temperature, the better the antistatic effect.
(1) Temperature change has little influence on the antistatic effect
In fact, at room temperature, the change of temperature has little effect on the antistatic effect, but the increase in temperature has a tendency to increase the antistatic performance because the migration of antistatic molecules increases with the increase of temperature.
(2) The change in humidity has a great influence on the antistatic effect.
Surface treatment with anti-static masterbatch leakage polymer surface charge, generally not only the conduction of electrons but also the movement of ionic charges. The charge movement is caused by the formation of hydrogen bonds by hydrophilic groups of anti-static masterbatch. Due to the hygroscopic properties of anti-static masterbatch, ionic groups can be produced after hygroscopic, which greatly improves the electrical conductivity of the plastic surface and promotes the play of the antistatic effect. Therefore, the higher the ambient humidity, the better the antistatic effect.
2. Affect the compatibility of resin
Plastic internal anti-static masterbatch using surfactants, this surfactant is mainly used through the internal molecular migration and conductive film formation on the surface.
(1) Good plastic compatibility affects the antistatic effect
If the plastic and the selected anti-static masterbatch compatibility is too good, the attraction between anti-static masterbatch molecules and the migration of anti-static masterbatch molecules is difficult to carry out, can not timely supplement the surface loss of anti-static masterbatch, it is difficult to play a good antistatic effect, must add too much anti-static masterbatch, but add too much, will also affect the other properties of plastic.
(2) poor compatibility will cause processing difficulties
If poor compatibility, often cause processing difficulties, at the same time, the anti-static masterbatch will be a large amount of precipitation, not only affecting the appearance of the product quality but also precipitating anti-static masterbatch will soon be lost, it is difficult to maintain a lasting antistatic effect.
(3) Appropriate anti-static masterbatch should be selected
Therefore, in the selection of suitable hydrophilic and lipophilic group groups, seeking appropriate compatibility between anti-static masterbatch and resin, the first consideration should be given to anti-static masterbatch, especially the molecular design of internal anti-static masterbatch. The two usually need to be mutually compatible and able to exude a certain amount of surface once they stop exuding.
After the loss of the surface anti-static masterbatch, the internal anti-static masterbatch can quickly ooze out of the surface and restore the antistatic effect, which is the ideal durability and anti-static property.
(4) The selection of a suitable anti-static masterbatch needs to do a lot of tests
The compatibility of anti-static masterbatch and resin depends on the molecular structure of polymer materials and the polarity of the anti-static masterbatch, the similar polarity is compatible, the polarity difference is not only difficult to mix, but also affects the quality and processing of the plastic surface.
In fact, it is difficult to choose the right compatibility and do a lot of tests.
3. The influence of polymer molecular structure
Among the parameters related to molecular structure, the glass transition temperature (Tg) is considered first. The anti-static masterbatch migrates to the plastic surface with the help of the movement of molecules in the chain of polymer compounds.
(1) The glass transition temperature affects the migration rate of antistatic molecules
The glass transition temperature of plastics directly affects the migration rate of antistatic molecules. Above the glass transition temperature, the polymer molecules move slightly Brownian, and an anti-static masterbatch is added to migrate to the surface with the help of the movement of molecular chain segments.
When the glass transition temperature is below, the polymer molecules freeze and the anti-static masterbatch is almost sealed between the polymer molecules, which is difficult to migrate to the surface.
(2) Lower glass transition temperature better antistatic
In general, in plastics with low glass transition temperature, such as PE, PP, soft PVC, etc., an anti-static masterbatch is easy to migrate to the surface, and antistatic property is easier to maintain. For plastics with high glass transition temperature, such as PS, ABS resin, hard PVC, PC, PET, etc., the anti-static masterbatch in these resins has poor permeability at room temperature.
During molding processing, the mold absorbs the anti-static masterbatch precipitation, transfers from the mold surface to the product surface, and forms an antistatic layer on the product surface. Anti-static masturbates with poor compatibility with resins, especially during hot working, will be transferred to the product surface in this way.
(3) The addition amount should be increased when the glass transition temperature is high
For plastics with a high glass transition temperature, when the glass transition temperature is higher, antistatic molecules also easily move to the surface along with polymer chain molecules. Of course, even at room temperature, when the polymer is in a stable state, there are molecules that migrate to the surface, just slowly.
In actual use, in addition to the molecular structure of anti-static masterbatch, the amount of plastics with high glass transition temperature needs to be appropriately increased. Sometimes, in order to speed up the migration rate, it can be heated at a temperature higher than the glass transition temperature and lower than the melting temperature to aggravate the movement of polymer molecules and promote the migration of anti-static masterbatches to the surface, in order to quickly display the antistatic properties.
In addition, the mobility of the anti-static masterbatch varies with the crystallization state of the polymer.
4. Influence of surface concentration of anti-static masterbatch
Distribution of anti-static masterbatch on the surface of plastic products, showing that the antistatic effect must reach a certain concentration, the concentration is called critical concentration. The critical concentration of various anti-static masterbatches varies depending on their chemical structure, composition, polarity, temperature, and use.
For general polymer compounds, it is about 0.5×10-2mg/cm2. Theoretically speaking, the anti-static masterbatch on the surface of the product only relies on the single molecule conductive layer formed by the hydrophilic group orientation in the air and has no obvious antistatic effect.
Because of the orientation of the hydrophilic group, an excellent antistatic effect will be produced when the surface is only 10 or more thick anti-static masterbatch molecular layer. Of course, the surface anti-static masterbatch concentration depends entirely on the rate of migration of antistatic molecules to the surface.
5. Influence of other additives
When processing polymer materials, add some stabilizer, pigment, plasticizer, lubricant, dispersant, or flame retardant. The interaction between these additives and the anti-static masterbatch will also have a great influence on the antistatic effect. For example, anion stabilizers and cationic anti-static masterbatch can easily compound with each other, reducing not only the antistatic properties but also the thermal stability.
(1) Anti-static masterbatch and slip masterbatch will interact
The slip masterbatch usually migrates quickly to the polymer surface, inhibiting the migration of the anti-static masterbatch. This is like covering a layer of lubricating oil on the antistatic layer, the surface concentration of the anti-static masterbatch decreases, which significantly affects the antistatic effect; In contrast, there is some slip masterbatch that facilitates the migration of anti-static masterbatch. In addition, surface lubrication film is formed to reduce friction, and the generation of electrostatic charge is also inhibited to a certain extent.
(2) Plasticizer is beneficial to the effect of anti-static masterbatch
Plasticizers will increase the distance between large molecular chains, making molecular movement easier, improving the polymer porosity, conducive to the anti-static masterbatch migration to the product surface, and playing an antistatic role.
Some plasticizers reduce the glass transition temperature of the polymer and also increase the antistatic effect. It is difficult to predict the influence of various additives on the antistatic properties in advance. At present, most of the anti-static masterbatch and their dosages are selected through experiments.
(3) Inorganic additives will weaken the antistatic effect
Inorganic additives, such as dispersants, stabilizers, and pigments, generally have strong adsorption capacity, so the anti-static masterbatch is difficult to migrate to the surface, and the diffusion and migration of the anti-static masterbatch has a reaction, the antistatic effect will become worse.
Most inorganic additives are small particles, have a large surface area, anti-static masterbatch easy adsorption, and can not effectively play an antistatic role. Pigment particles tend to be abundant around anti-static masterbatch, affecting their outward diffusion. For example, the same concentration of anti-static masterbatch ABS titanium dioxide is added to reduce the antistatic effect. Different inorganic fillers have different adsorbability and different influences on the antistatic effect.
(4) halogenated flame retardants will reduce the efficiency of nonionic anti-static masterbatch
The elastomer in the polymer also reduces the efficiency of the anti-static masterbatch. For example, in composites of polypropylene and rubber, anti-static masterbatches are found around the rubber component, making it difficult to migrate to the surface.
In the actual formulation of an anti-static masterbatch, special attention is paid to the interaction with other additives.
6. Influence of the processing process
In different processing methods of antistatic products, the dispersion state and migration rate of anti-static masterbatch are different, and the antistatic effect is different. If the polymer is formed in the melting state, it is cooled immediately at room temperature lower than the glass transition temperature. The anti-static masterbatch is difficult to spread to the surface of the product, and the antistatic effect is not enough. If the product is cooled at an environment higher than the glass transition temperature, because the movement of the macromolecular chain segment helps the antistatic diffusion, not only the product can show enough antistatic effect, even the use of friction or water to clean the surface of the anti-static masterbatch, its antistatic effect can be quickly restored.
In addition, appropriate treatment of the plastic surface, if the surface is partially oxidized, can produce a polarity group, it is often stacked with an anti-static masterbatch, giving full play to the antistatic effect. For different resins, to achieve the same antistatic effect, the amount of anti-static masterbatch is different. Therefore, the design and use of an anti-static masterbatch should consider the above factors, through the experiment to screen the variety and the best dosage of anti-static masterbatch.